Method for cooling an internal combustion engine having exhaust gas recirculation and charge air cooling

ABSTRACT

A system for cooling charge air from a turbo- or supercharger and exhaust gas recirculated from an exhaust gas recirculation valve in an internal combustion engine. The system includes a radiator and parallel charge air and exhaust gas heat exchanger units, the charge air heat exchanger unit having aluminum tubes and fins for air cooling the charge air, and the exhaust gas heat exchanger unit having stainless steel tubes and fins. The charge air heat exchanger and the exhaust gas heat exchanger units are each disposed adjacent the radiator, on the same or opposite sides. Alternatively, there is provided a pair of combined charge air cooler and exhaust gas cooler heat exchanger units, with a first heat exchanger unit having stainless steel tubes and fins, and a second heat exchanger unit having aluminum tubes and fins. The heat exchanger units are disposed on opposites sides of the radiator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a cooling system for internal combustionengines used in trucks and other motor vehicles and, in particular, to acooling system utilizing a charge air cooler and an exhaust gas coolerin combination with a radiator.

2. Description of Related Art

Stricter emissions requirements have forced the use of partial exhaustgas recirculation as a means of achieving more complete combustion, andthis has necessitated the cooling of the recirculated exhaust gas beforeintroducing it into the engine intake manifold. FIG. 1 shows a typicalheavy duty truck cooling system having a liquid-cooled exhaust gasrecirculation (EGR) cooler. The engine cooling system comprises aninternal combustion engine 20 utilizing conventional liquid enginecoolant. The liquid coolant heated by operation of the engine exits theengine through line or hose 61 and passes through a thermostat 30. Ifthe coolant is below the thermostat set temperature it is passed throughline 63 to coolant pump 32 and back through line 65 to the engine. Ifthe coolant is above the thermostat set temperature, it is sent throughline 62 to otherwise conventional air cooled radiator 22 where ambientair flow 60, 60 a and 60 b passes through the radiator by means of a fan(not shown) as well as movement of the vehicle in which the engine ismounted. The cooled liquid coolant then passes through lines 57 and 59back to the coolant pump before returning to the engine.

For mixture with the fuel, the engine utilizes inlet air 40 that passesthrough a filter (not shown) and is compressed by a turbo- orsupercharger. The engine system depicted herein utilizes engine exhaustgases exiting through lines 50 and 54 in a turbocharger in which turbine26 drives compressor 28. After passing through the turbine blades, theexhaust gas exits through line 55 to the exhaust system (not shown).After compression, the charge air passes through line 42 to air-to-aircharge air cooler (CAC) 24 mounted upstream of radiator 22. The cooledcharge air then exits CAC 24 through line 44.

A portion of the exhaust gas exiting through line 50 passes through line52 and through an EGR valve 48. The exhaust gas then passes through line56 to EGR cooler 34, which is a liquid-to-air heat exchanger that coolsthe hot exhaust gases using the cooled liquid engine coolant enteringthrough line 57. Because brazed aluminum heat exchanger construction isnot capable of withstanding the high exhaust gas temperatures,typically, such an EGR cooler must be of high-temperature heat exchangerconstruction; that is, made of materials able to withstand highertemperatures than brazed aluminum, such as brazed stainless steel,brazed cupro-nickel, brazed copper, and the like. The cooledrecirculated exhaust gas then exits the EGR cooler through line 58,where it mixes with the cooled charge air from line 44. The mixture ofcooled recirculated exhaust gas and charge air then proceeds throughline 46 to the intake manifold 21 of engine 20 for mixture with the fueland then to the engine combustion chambers.

This system has two disadvantages: 1) the high cost of stainless steelor other high temperature EGR cooler construction and 2) the coolinglimitation resulting from the use of engine coolant at approximately180° F.

FIG. 2 shows another prior art heavy duty truck cooling system in whichthe exhaust gas which is to be recirculated is mixed with the hot chargeair coming from the turbocharger for cooling in an air-cooled heatexchanger. Since the liquid engine coolant does not need to cool theexhaust gas, the liquid engine coolant passes through line 57 fromradiator 22 and back to coolant pump 32 for return to the engine. Thehot exhaust gas exiting EGR valve 48 passes through line 56 where itcombines and mixes with compressed, heated charge air in line 41 exitingcompressor 28. The combined heated exhaust gas and charge air thenpasses through line 43 to a brazed stainless steel combination exhaustgas recirculation and charge air cooler 24′ upstream of radiator 22.Alternatively, the combination exhaust gas recirculation and charge aircooler may be made of other high temperature construction such as theaforementioned brazed cupro-nickel or brazed copper. After the chargeair and exhaust gas are cooled by ambient air 60 passing through CAC24′, the cooled combined exhaust gas and charge air then pass throughline 45 to engine intake manifold 21. This approach does allow therecirculated exhaust gas and charge air to be cooled to a temperatureclose to that of the ambient cooling air, which will always be much lessthan that of the engine coolant. However, it does not solve the expenseproblem related to high temperature-resistant construction and, in fact,increases the expense by requiring stainless steel or other expensivehigh temperature material to be used in a very large combinationEGR/CAC.

In addition to having high material costs, prior systems and methods ofcooling charge air and/or recirculated exhaust gases in an internalcombustion engine have not been able to individually tailor thermalperformance of individual heat exchanger units in a space-savingpackage.

SUMMARY OF THE INVENTION

Bearing in mind the problems and deficiencies of the prior art, it istherefore an object of the present invention to provide an improvedsystem and method of cooling an internal combustion engine, includingcharge air cooling and exhaust gas cooling, which achieves cooling ofthe charge air and the recirculated exhaust gas to near ambienttemperatures.

It is another object of the present invention to provide a system andmethod of cooling an internal combustion engine, including charge aircooling and exhaust gas cooling, which allows the use of lower costmaterials for the charge air and exhaust gas coolers.

A further object of the present invention is to provide a system andmethod of cooling charge air and recirculated exhaust gas in an internalcombustion engine which saves space in a combined radiator, CAC and EGRcooler package.

Yet another object of the present invention is to provide a combinedheat exchanger package for an internal combustion engine that permitstailoring of thermal performance of individual heat exchanger unitswithin the package.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The above and other objects, which will be apparent to those skilled inthe art, are achieved in the present invention which is directed to amethod and apparatus for cooling charge air from a turbo- orsupercharger and exhaust gas recirculated from an exhaust gasrecirculation valve in an internal combustion engine comprisingproviding a radiator for air cooling of liquid engine coolant from theinternal combustion engine and providing parallel charge air and exhaustgas heat exchanger units. The charge air heat exchanger unit hasaluminum tubes and fins for air cooling the charge air, and the exhaustgas heat exchanger unit having tubes and fins made of a materialresistant to higher operating temperatures than aluminum for air coolingthe exhaust gas. The charge air heat exchanger and the exhaust gas heatexchanger units are each disposed adjacent a face of the radiator topermit ambient air to flow in series through the radiator and the chargeair and exhaust gas heat exchanger units. The method then includespassing the charge air from the turbo- or supercharger through thecharge air heat exchanger unit to cool the charge air, passing theexhaust gas from the exhaust gas recirculation valve through the exhaustgas heat exchanger unit to cool the exhaust gas, and combining thecooled charge air and cooled exhaust gas for passage into an intakemanifold on the engine.

Preferably, the exhaust gas heat exchanger unit has tubes and fins madeof stainless steel. The radiator may comprise two units, with the chargeair heat exchanger unit being disposed adjacent a face of one radiatorunit and the exhaust gas heat exchanger unit being disposed adjacent aface of the other radiator unit. The charge air heat exchanger unit andthe exhaust gas heat exchanger unit may have different core styles, suchas different core depth, type of fins, fin spacing, fin count, tubespacing and tube count.

The charge air and exhaust gas heat exchanger units may be disposed inparallel adjacent a same face of the radiator to permit ambient air toflow in series through the radiator and the charge air and exhaust gasheat exchanger units.

The charge air and exhaust gas heat exchanger units may be disposeddownstream of the radiator with respect to ambient air flow to permitambient air to flow in series first through the radiator andsubsequently through the charge air and exhaust gas heat exchangerunits, or vice-versa.

The charge air and exhaust gas heat exchanger units may be disposedadjacent opposite faces of the radiator, with the charge air heatexchanger unit being disposed upstream of the radiator and the exhaustgas heat exchanger unit being disposed downstream of the radiator. Thispermits ambient air to flow in series first through charge air heatexchanger unit having aluminum tubes and fins and then through theradiator, and permits ambient air to flow in series through the radiatorand subsequently through the exhaust gas heat exchanger unit havingtubes and fins made of the higher temperature resistant material. Theradiator may alternately comprise two units, with the charge air heatexchanger unit being disposed upstream adjacent one radiator unit andthe exhaust gas heat exchanger unit being disposed downstream adjacentthe other radiator unit. The charge air heat exchanger unit and theexhaust gas heat exchanger unit may have different core styles, and eachradiator unit may have a different core style.

Alternatively, the charge air and exhaust gas heat exchanger units maybe a first set disposed downstream of the radiator with respect toambient air flow to permit ambient air to flow in series first throughthe radiator and subsequently through the first set of charge air andexhaust gas heat exchanger units. There may be further provided a secondset of charge air and exhaust gas heat exchanger units, wherein bothheat exchanger units in the second set have aluminum tubes and fins forair cooling the charge air and the exhaust gas. The second set of chargeair and exhaust gas heat exchanger units are disposed upstream of theradiator to permit ambient air to flow in series first through thesecond set of charge air and exhaust gas heat exchanger units andsubsequently through the radiator. The partially cooled charge air fromthe charge air heat exchanger unit downstream of the radiator is passedthrough the second charge air heat exchanger unit upstream of theradiator to further cool the charge air. The partially cooled exhaustgas from the exhaust gas heat exchanger unit downstream of the radiatoris passed through the second exhaust gas heat exchanger unit upstream ofthe radiator to further cool the exhaust gas before combining the cooledcharge air and cooled exhaust gas for passage to the intake manifold ofthe engine. At least one of the charge air heat exchanger units orexhaust gas heat exchanger units may have a different core style. Theradiator may comprises two units, with the first set of charge air andexhaust gas heat exchanger units downstream of the radiator beingdisposed adjacent one radiator unit and the second set of charge air andexhaust gas heat exchanger units upstream of the radiator being disposedadjacent the other radiator unit. Each radiator unit may have adifferent core style.

In another aspect, the present invention is directed to a method andapparatus for cooling charge air from a turbo- or supercharger andexhaust gas recirculated from an exhaust gas recirculation valve in aninternal combustion engine comprising providing a radiator for aircooling of liquid engine coolant from the internal combustion engine andproviding a pair of combined charge air cooler and exhaust gas coolerheat exchanger units. A first one of the heat exchanger units has tubesand fins made of a material able to withstand higher operatingtemperatures than aluminum, and the second of the heat exchanger unitshas aluminum tubes and fins. The heat exchanger units are disposedadjacent the radiator to permit ambient air to flow in series throughthe radiator and the heat exchanger units. The method includes combiningthe charge air from the turbo- or supercharger with the exhaust gasrecirculated from the exhaust gas recirculation valve, passing thecombined charge air and exhaust gas through the first heat exchangerunit having the tubes and fins made of the higher temperature resistantmaterial to partially cool the combined charge air and exhaust gas,passing the partially cooled combined charge air and exhaust gas throughthe second heat exchanger unit having the aluminum tubes and fins tocool the combined charge air and exhaust gas, and passing the combinedcooled charge air and exhaust gas into an intake manifold on the engine.

The heat exchanger unit having tubes and fins made of the highertemperature resistant material, preferably stainless steel, may bedisposed downstream of the radiator with respect to ambient cooling airflow to permit ambient air to flow in series first through the radiatorand subsequently through the heat exchanger unit having tubes and finsmade of the higher temperature resistant material. The heat exchangerunit having aluminum tubes and fins may be disposed upstream of theradiator with respect to ambient cooling air flow to permit ambient airto flow in series first through the heat exchanger unit having aluminumtubes and fins and subsequently through the radiator.

The radiator may comprises two units, with the first heat exchanger unitbeing disposed adjacent a face of one radiator unit and the second heatexchanger unit being disposed adjacent a face of the other radiatorunit. Each of the first and second heat exchanger units may have adifferent core style, and each radiator unit may have a different corestyle.

In a further aspect, the present invention provides a method andapparatus for cooling engine coolant and charge air from a turbo- orsupercharger in an internal combustion engine comprising providing aradiator for cooling engine coolant having opposite front and rear corefaces through which ambient air flows, and opposite upper and lower endsadjacent the faces, and providing a charge air cooler for cooling chargeair having upper and lower units. Each charge air cooler unit hasopposite front and rear core faces through which ambient air may flow,and opposite upper and lower ends adjacent the faces. The upper chargeair cooler unit is disposed in overlapping relationship and adjacent tothe upper end of the radiator, wherein one face at the upper end of theradiator is disposed adjacent one face of the upper charge air coolerunit, and the lower charge air cooler unit is disposed in overlappingrelationship and adjacent to the lower end of the radiator with theupper and lower ends of the lower charge air cooler unit being orientedin the same direction as the upper and lower ends of the radiator,wherein the other face at the lower end of the radiator is disposedadjacent one face of the lower charge air cooler unit. Each charge aircooler unit has a different core style selected from the groupconsisting of core depth, type of fins, fin spacing, fin count, tubespacing and tube count. The charge air cooler units are operativelyconnected such that the charge air may flow therebetween. The methodincludes flowing the engine coolant through the radiator to cool theengine coolant, flowing the charge air from the turbo- or superchargerin sequence through the charge air heat exchanger units to cool thecharge air, and flowing cooling air through the heat exchanger assemblysuch that the cooling air flows in series through the upper end of theradiator and the upper charge air cooler unit, and the cooling air flowsin series through the lower charge air cooler unit and the lower end ofthe radiator. At least one of the charge air cooler units may includecooling for recirculated exhaust gas.

In yet another aspect, the present invention provides a method andapparatus for cooling engine coolant and charge air from a turbo- orsupercharger in an internal combustion engine comprising providing aradiator having upper and lower units for cooling engine coolant, witheach radiator unit having opposite front and rear core faces throughwhich ambient cooling air flows, a depth between the front and rearfaces, and opposite upper and lower ends adjacent the faces. Theradiator units are operatively connected such that the engine coolantmay flow therebetween. There is also provided a charge air cooler havingupper and lower units for cooling charge air, with each charge aircooler unit having opposite front and rear core faces through whichcooling air may flow, and opposite upper and lower ends adjacent thefaces. The upper charge air cooler unit is disposed in overlappingrelationship and adjacent to the upper radiator unit with the upper andlower ends of the upper charge air cooler unit, wherein one face of theupper radiator unit is disposed adjacent one face of the upper chargeair cooler unit, and the lower charge air cooler unit is disposed inoverlapping relationship and adjacent to the lower radiator unit,wherein the other face of the lower radiator unit is disposed adjacentone face of the lower charge air cooler unit. Each charge air coolerunit has a different core style selected from the group consisting ofcore depth, type of fins, fin spacing, fin count, tube spacing and tubecount. The charge air cooler units are operatively connected such thatthe charge air may flow therebetween. The method then includes flowingthe engine coolant in sequence through the radiator units to cool theengine coolant, flowing the charge air from the turbo- or superchargerin sequence through the charge air heat exchanger units to cool thecharge air, and flowing cooling air through the heat exchanger assemblysuch that the cooling air flows in series through the upper radiatorunit and the upper charge air cooler unit, and the cooling air flows inseries through the lower charge air cooler unit and the lower radiatorunit. At least one of the charge air cooler units may include coolingfor recirculated exhaust gas. Each radiator unit may have a differentcore style.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a partially schematic view of a prior art internal combustionengine cooling system.

FIG. 2 is a partially schematic view of another prior art internalcombustion engine cooling system showing in side elevational view therelative placement of a combined exhaust gas and charge air cooler withrespect to the radiator.

FIG. 3 is a graphical depiction of percent of maximum heat transfer as afunction of number of rows of tubes in a single heat exchanger core.

FIG. 4 is a partially schematic view of one embodiment of the internalcombustion engine cooling system of the present invention showing inside elevational view the relative placement of exhaust gas and chargeair coolers with respect to the radiator.

FIG. 5 is a perspective view of the charge air cooler and EGR gas coolerused in some embodiments of the internal combustion engine coolingsystem of the present invention. FIG. 5 a is a modification of FIG. 5,and shows different core depths, different tube spacing and differenttube count for the charge air cooler and EGR cooler.

FIG. 6 is a partially schematic view of another embodiment of theinternal combustion engine cooling system of the present inventionshowing in side elevational view the relative placement of an exhaustgas cooler and a charge air cooler with respect to the radiator.

FIG. 7 is a side elevational view of a modification of theradiator/charge air cooler and exhaust gas cooler package of FIG. 6,where the radiator is split into two units, and the entire package istwo cores deep.

FIG. 8 is a partially schematic view of a further embodiment of theinternal combustion engine cooling system of the present inventionshowing in side elevational view the relative placement of combinedexhaust gas and charge air coolers with respect to the radiator.

FIG. 9 is a side elevational view of a modification of theradiator/charge air cooler and exhaust gas cooler package of FIG. 8,where the radiator is split into two units, and the entire package istwo cores deep.

FIG. 10 is a sectional plan view of portions of the cores of the upperand lower combined EGR/CAC radiator units of FIG. 9 showing differencesin tube spacing, tube minor diameter and core depth.

FIG. 11 is a sectional elevational view of portions of the cores of theupper and lower combined EGR/CAC radiator units of FIG. 9 showingdifferences in fin count, fin thickness and fin louver angle.

FIG. 12 is a partially schematic view of yet another embodiment of theinternal combustion engine cooling system of the present inventionshowing in side elevational view the relative placement of exhaust gasand charge air coolers with respect to the radiator.

FIG. 13 is a side elevational view of a modification of theradiator/charge air cooler and exhaust gas cooler package of FIG. 12,where the radiator is split into two units, and the entire package istwo cores deep.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In describing the preferred embodiments of the present invention,reference will be made herein to FIGS. 3-13 of the drawings in whichlike numerals refer to like features of the invention.

The management of airflow through an air cooled heat exchanger orpackaged group of heat exchangers is important to the heat transferperformance of the heat exchanger unit or package. The development ofairflow paths that optimize temperature potential is vital in the designof space-saving cooling systems within the constraints of typicalfan/shroud arrangements in heavy-duty trucks.

Before considering airflow in the EGR/CAC/radiator heat exchangerpackages disclosed herein, it is useful to examine airflow in a singlecore heat exchanger. FIG. 3 depicts the relationship of heat transfer asa function of number of rows of tubes in a heat exchanger core. Avehicle radiator having only one row of core tubes is initially assumed,wherein the depth in the direction of airflow is 0.50 in. (13 mm). Ifthe tube spacing across the face of the core is about 0.44 in. (11 mm)and the fin spacing is about 14 fins per in. (5.5 fins/cm), then theairflow through the core, caused either by the action of a fan or by ramair as a result of vehicle motion, will be reasonably high. If increasedheat transfer performance is desired, a radiator with an additional rowof tubes may be used, making the core two rows deep. The cooling airflowwill decrease slightly because of the added resistance of the deepercore, but the overall heat transfer will be greatly increased. However,as illustrated in FIG. 3, as the core is made even deeper, to three,four, five and six rows deep, cooling air flow is greatly reduced, tothe point where adding another row will result in decreased, rather thanincreased, heat transfer performance. This occurs because with the lowairflow and deep core, the cooling air reaching the last row of tubes isalready heated to the point where it is ineffective in creating furthercooling. In such a case, improved performance can be achieved byreducing the core depth to manage, or increase, the cooling airflow, andby other methods and means, discussed further below.

The internal combustion engine cooling system of the present inventionachieves cooling of the charge air and the recirculated exhaust gas tonear ambient temperatures, but permits the use of lower cost materialsoverall. FIG. 4 shows a first embodiment of the cooling system in whichthe air-cooled stainless steel or other high temperature-resistantexhaust gas cooler is separate from, and in parallel with, an aluminumcharge air cooler, with respect to the cooling ambient air flow. As usedherein, the term “ambient air” includes all of the cooling air as itpasses through the radiator, exhaust gas cooler and charge air coolerheat exchanger units, even though it is heated as it passes through thefins of the heat exchanger units. Instead of combining the hot exhaustgas from EGR valve 48 with the heated charge air, or separately coolingthe heated exhaust gas utilizing the liquid engine coolant, the heatedexhaust gas passes through line 56 to an air-to-air exhaust gas heatexchanger 70 for cooling. The term “line” as used herein is intended toinclude hoses, tubing, piping and the like typically used to carryfluids in an internal combustion engine environment, such as the exhaustgas, charge air and liquid coolant described herein. Exhaust gas cooler70 is disposed upstream of radiator 22 and receives inlet ambientcooling air 60. Radiator 22 is typically a down flow type radiator,wherein engine coolant enters through an upper manifold extendingsubstantially the entire width of the radiator, is then distributed inthe core through vertical, downwardly extending tubes connected bycooling fins, so that ambient cooling air may flow from the front face23 a of the core through and out of the rear face 23 b. After beingcooled by the ambient air, the coolant then collects in an attachedlower manifold also extending across the width of the radiator.Alternatively, the radiator may be an up-flow type radiator, withcoolant flow in the opposite direction, or a cross flow type radiatorwith coolant flow through core tubes extending horizontally betweenhorizontally opposed manifolds.

In parallel with and above exhaust gas cooler 70, and also in front ofand in series with radiator 22 with respect to the ambient air flow,charge air cooler heat exchanger 80 receives the heated, compressedcharge air through line 42, where it is also cooled by ambient air 60entering through the CAC/EGR cooler front face 77 a. As a result,ambient air 60 a exiting from the CAC/EGR cooler rear face 77 b isheated by both the exhaust gas and charge air coolers before it passesthrough radiator 22, where it is further heated and exits 60 b from theradiator. The cooled exhaust gas exits exhaust gas cooler 70 throughline 58, and the cooled charge air exits charge air cooler 80 throughline 44. The cooled charge air then combines with the cooled exhaust gasand passes through line 46 to engine intake manifold 21. Alternatively,the EGR cooler 70 and CAC 80 may be disposed on the opposite side ofradiator 22, i.e., downstream of the radiator with respect to theambient air flow.

In this embodiment, the recirculated exhaust gas and the charge air arecombined after the charge air cooler, rather than before it as in theprior art system of FIG. 2. This system and method avoid having to makea combination exhaust gas and charge air cooler entirely out ofstainless steel or other high temperature-resistant material. Instead,while the exhaust gas cooler is still made of stainless steel or thelike, the charge air cooler may be made of aluminum.

The radiator, CAC and EGR cooler shown in the embodiment of FIG. 4 (aswell as in the subsequent embodiments described below) are preferablysecured to each other to create a combined heat exchanger package. Theair-to-air heat exchanger units used for the exhaust gas cooler 70 andcharge air cooler 80 are shown in more detail in FIG. 5. Charge aircooler 80 includes upper and lower horizontally extending manifolds 81,82 respectively, which distribute or collect the charge air passingthrough spaced, vertically extending tubes 83 connecting the manifolds.These tubes may be two (2) rows deep, as shown in FIG. 5, or any otherconfiguration, to achieve desired core depth d₁. A serpentine coolingfin array 84 (also of depth d₁) between adjacent tubes 83 extendingacross the face of charge air cooler 80 comprises the charge air coolercore, which transfers the heat from the charge air within the tubes tothe ambient air passing between the tubes 83 and over the fins 84. Thevertical spacing between the serpentine fins determines the desired fincount. The fins may be of the louvered, lanced-offset, wavy(non-louvered) or other type, or plate fins may be used instead. Themanifolds have openings 85, 86 for passage of charge air into or out ofthe manifolds. The CAC may be configured as an upflow unit, where heatedcharge air is received in inlet 86 of manifold 82 where it passes upwardthrough tubes 83 and from manifold 81 through outlet 85 as cooled chargeair. Alternatively, the CAC may be configured as a downflow unit, wherethe heated charge air flow is received in inlet 85 and flows in areverse direction out through outlet 86 as cooled charge air.

In a construction analogous to that of the charge air cooler, exhaustgas cooler 70 has upper and lower manifolds 71 and 72, with the formerhaving inlet/outlet 75 and the latter having inlet/outlet 76. Tubes 73carry the exhaust gas between manifolds 71 and 72, and fins 74 betweenadjacent tubes 73 permit passage of the cooling ambient air therebetweento cool the hot exhaust gases passing within tube 73. The core has depthd₂, and tubes 73 and fins 74 may be modified as described in connectionwith CAC 80. As with the charge air cooler, EGR cooler 70 may be set upas a downflow unit, so that the hot exhaust gases are passed throughinlet 75 downward through the tubes and cooled exhaust gas passesoutward through outlet 76, or as an upflow unit where the exhaust gastravels in the reverse direction.

As shown in FIG. 5, both exhaust gas cooler 70 and charge air cooler 80have a horizontal width, measured in the direction of the manifolds,which is greater than the vertical height of each of the units, measuredbetween the manifolds. Improved heat exchanger performance as a resultof reduced charge air pressure drop, may be obtained by utilizing tubeswhich are as short as possible and as numerous as possible, given theconfiguration of the heat exchanger units. As shown in this embodiment,both the exhaust gas and charge air coolers employ tubes which areoriented with the shorter vertical height of each of the units so thatthere is a larger number of shorter tubes. Alternatively, both theexhaust gas and charge air coolers may be cross-flow units with exhaustgas flow through horizontally oriented tubes extending betweenvertically oriented manifolds on either side of the charge air cooler.

Preferably, charge air cooler 80 and exhaust gas cooler 70 are sized sothat their respective widths w₁ and w₂ are each the same as the width ofthe radiator with which they are packaged. Preferably, CAC 80 and EGRcooler 70 are connected to each other, as indicated by the arrows, tocreate a single unit that is positioned adjacent to the radiator. Thecombined heights of the charge air cooler 80 and EGR cooler 70, h₁ andh₂ respectively, may be up to the height of the radiator. Typically, theheight h₁ of the charge air cooler is greater than the height h₂ of theexhaust gas cooler 70 when there are greater cooling requirements forthe charge air versus the recirculated exhaust gas.

In addition to modifying the heights and widths of the CAC and EGRcoolers, the cores of each may be modified as desired to achieve thedesired thermal cooling properties for the combined radiator/CAC/EGRcooler package. For example, the core depths, the type of fins, the finspacing and count, and the tube spacing and count for each CAC and EGRcooler may be the same as or different from other CAC and EGR coolers inthe package. FIG. 5 a is a modification of FIG. 5, and shows differentcore depths d₁′ and d₂′, and different tube spacing and different tubecount across the widths w₁ and w₂ of the CAC unit 80 and EGR cooler unit70, respectively.

The manifolds, tubes and fins of charge air cooler 80 may be made ofaluminum, either as a conventional fully brazed CAC or with brazed tubesand fins and grommeted tube-to-header joints. The latter is disclosed inU.S. Pat. Nos. 5,894,649, 6,330,747 and 6,719,037, the disclosures ofwhich are hereby incorporated by reference. Because the exhaust gases tobe cooled are considerably hotter than the charge air to be cooled bycharge air cooler 80, exhaust gas cooler 70 is preferably not made ofaluminum, and instead the manifolds, tubes and fins are made ofstainless steel or other high temperature-resistant material foradditional heat resistance and product life. Since only the portion ofthe heat exchanger package used to cool the exhaust gas is made ofstainless steel or the like, the cost of the combined exhaust gas cooler70 and charge air cooler 80 is less, since the charge air cooler portionis made of lower cost aluminum.

FIG. 6 depicts another embodiment of the cooling system of the presentinvention. Instead of combining the exhaust gas cooler with the chargeair cooler in a common unit adjacent the same face of the radiator,exhaust gas cooler 70 is placed adjacent the face of the radiatoropposite the charge air cooler, which is disposed near the upper end ofthe radiator. As with the previous embodiment, charge air cooler 80 isdisposed upstream of radiator 22 so that ambient air 60 passes throughfront face 87 a and out of rear face 87 b as partially heated ambientair 60 a. The height of the charge air cooler 80 is less than that ofradiator 22, so that a portion of radiator 22 (here shown as the lowerportion) receives ambient air 60 which does not pass through the chargeair cooler. The remaining portions of the radiator 22 receive ambientair 60 a which has been heated partially by passage in series throughcharge air cooler 80. Disposed downstream of radiator 22 is exhaust gascooler 70, here shown disposed adjacent to the lower portion of theradiator 22 which receives the unheated ambient air 60. The ambient air60 b partially heated after passage through rear face 23 b of radiator22 then passes in series through the front face 77 a and the fins andtubes of exhaust gas cooler 70, and exits 60 c at a higher temperaturefrom rear face 77 b. However, the difference in temperature between theexhaust gas and the heated cooling air 60 b is still sufficient to allowgood heat transfer. The cooled exhaust gas exits the cooler 70 andpasses through line 58 where it combines with the cooled charge air inline 44. The combined mixture then passes through line 46 into engineintake manifold 21.

The height h₁ of charge air cooler 80 and the height h₂ of exhaust gascooler 70 are preferably selected so that the combined height h₁+h₂ isapproximately equal to the height of radiator 22, and the two coolers70, 80 do not overlap with each other. Placing the exhaust gas coolerbehind the radiator in this embodiment improves the radiator coolingperformance by avoiding heating of the radiator by the exhaust gascooler. As with the previous embodiment, exhaust gas cooler 70 is madeof stainless steel or other high temperature-resistant material and thecharge air cooler 80 is made of lower cost aluminum.

A modification of the embodiment of FIG. 6 is shown in FIG. 7, wherecharge air cooler 80 and exhaust gas cooler 70 are the same, but theradiator is split into two different portions or units, upper rear unit22 a and lower front unit 22 b, in a manner similar to that shown inU.S. Patent Publication No. US2005-0109484-A1, the disclosure of whichis hereby incorporated by reference. In the front (with respect toambient air flow 60), charge air cooler 80 is above and has front andrear faces substantially planar with those of lower radiator unit 22 b,and in the rear exhaust gas cooler 70 is below and has front and rearfaces substantially planar with those of upper radiator unit 22 a.Variations in core depth in the individual units may change the planaralignment slightly. The heights and widths of upper radiator unit 22 aand charge air cooler 80 are substantially the same, as are the heightsand widths of lower radiator unit 22 b and exhaust gas cooler 70. Eachradiator unit 22 a, 22 b has a construction similar to the full radiatorpreviously described above, but with shorter height. As in the case ofthe CAC and EGR coolers described in FIG. 5, the core of each unit 22 a,22 b may be varied in depth, type of fins, fin spacing and count, andtube spacing and count, compared to the other, to achieve the desiredbalance of thermal cooling properties in the package. An additional line62 a passes partially cooled engine coolant from upper unit 22 a tolower unit 22 b. The modification in FIG. 7 results in a combinedradiator/CAC/EGR cooler package that is only two cores deep, as opposedto the three core deep package of FIG. 6. This saving in core depth hasbenefits in that fan 90 exhausting the heated ambient air 60 d may bespaced farther back from the rear core face, and thereby provide forhigher air flow and better air flow distribution over the entire coreface of the heat exchanger package.

A further embodiment of the present invention is depicted in FIG. 8.Instead of cooling the exhaust gas and heated charge air in separateheat exchangers, the heated exhaust gas from line 56 is combined withthe heated charge air exiting the compressor in line 41, and the mixtureof heated exhaust gas and charge air passes through line 43 to firstcombined exhaust gas and charge air cooler 80 a. Combined exhaust gasand charge air cooler 80 a is disposed downstream of radiator 22, in alocation corresponding to the lower portion of the radiator 22 thatreceives fresh ambient cooling air 60 through front face 23 a. Afterambient air 60 passes through the radiator rear face 23 b and exits aspartially heated ambient air 60 b, it then passes in series through thefront face 87 a and the fins and tubes of the combined cooler 80 a andexits as heated ambient air 60 c from the rear face 87 b. The combinedcooler 80 a is constructed in a manner similar to charge air cooler 80shown in FIG. 5, except that it is made of stainless steel or other hightemperature-resistant material instead of aluminum since it is carryinggases at a higher temperature.

As it exits cooler 80 a, the combined exhaust gas and charge air ispartially cooled. It then travels through line 69 where it then enters asecond combined exhaust gas and charge air cooler 80 b, disposedupstream of radiator 22. Combined cooler 80 b is shown adjacent thefront face 23 a, near the upper portion of radiator 22 so that it doesnot overlap with the first combined cooler 80A adjacent the rear face 23b, near the lower portion of radiator 22. The partially cooled combinedexhaust gas and charge air is then subject to maximum cooling by ambientair 60, which passes through the front face 87 a and the tubes and finsof cooler 80 b, and exits rear face 87 b as heated ambient air 60 a tocool radiator 22 in series. The arrangement of this split exhaust gasand charge air cooler is similar to that of the split charge air coolerdisclosed in U.S. Patent Publication No. US2005-0109483-A1, thedisclosure of which is hereby incorporated by reference. The cooledcombined exhaust gas and charge air then exits cooler 80 b through line45 to intake manifold 21. Since the combined exhaust gas and charge airreceived in cooler 80 b is already partially cooled, cooler 80 b doesnot need to be made of stainless steel or other hightemperature-resistant material, and can be made of aluminum. Preferably,heights and locations of coolers 80 a and 80 b are selected so that theydo not overlap with one another, and their combined heights areapproximately equal to the height of radiator 22. Additionally, the corestyles, i.e., the core depth, the type of fins, the fin spacing andcount, and the tube spacing and count, may be varied and tailored foreach unit 80 a, 80 b, to obtain the desired air flow split and unitperformance. For example, the front unit 80 b may have a lower fin countand/or core depth (the latter shown by the reduced core depth of frontface 87 a′) to limit the heating of the ambient air that passes throughthe core of the radiator, whereas the rear unit 80 a may have a higherfin count and/or core depth (the latter shown by the increased coredepth of rear face 87 b′) to derive maximum cooling of the combinedexhaust gas and charge air. Effects of variation in core parameters arediscussed further below. This system and method provides maximum heattransfer performance with material cost savings over the prior artsystem and method of FIG. 2 because at least half of the combinedexhaust gas and charge air cooler can be made with the lower costaluminum construction.

FIG. 9 shows a modification of the embodiment of FIG. 8. In a mannersimilar to the modification of FIG. 7, the radiator is split into twounits 22 a, 22 b, with connecting line 62 a, so that the combinedradiator/CAC/EGR cooler package is only two cores deep with respect toambient air flow 60. Again, the front and rear faces of the verticallymatched units 80 b, 22 b and 22 a, 80 a, respectively, are insubstantially the same planes (except for any variations in core depthin the individual units) and the heights and widths of the horizontallymatched units, 22 a, 80 b and 80 a, 22 b, respectively, aresubstantially the same. This again saves space and permits more optimalmounting of fan 90 for better flow through the package of the coolingambient air.

In a packaged group of heat exchangers, as depicted in FIGS. 4, 6, 7, 8and 9, it is particularly important to manage the airflow splits amongthe various heat exchangers in order to achieve optimum heat transferperformance. In a package with split radiator and split charge aircooler as shown in FIG. 9, it may be desirable, in order to achieveoptimum radiator performance, to manage the cooling airflow through thefront charge air cooler by lowering its core resistance. This willresult in the minimum impact of the front charge air cooler upon theradiator core behind, and will provide optimized cooling airflow to theradiator, resulting in optimum radiator heat transfer.

The flow of cooling air through a heat exchanger core, for example thecores of radiator units 22 a, 22 b and charge air cooler units 80 a, 80b, may be managed in a number of different ways, each affecting the coreairflow resistance or the airflow resistance of the entire airflow path.For example, airflow through a given heat exchanger may be increased byincreasing the core resistance of a heat exchanger in parallel with itor by decreasing its own core resistance or the core resistance of aheat exchanger in series with it. Various core parameters may be variedin any of the heat exchangers of FIGS. 4, 6, 7, 8 and 9 to achieve afin/tube system with the desired cooling airflow resistance.

As described above in connection with FIG. 9, and as shown in FIG. 10where the cores of the upper and lower combined EGR/CAC units arejuxtaposed for comparison, a decreased depth d of the core of uppercombined exhaust gas and charge air cooler unit 80 b (in front of theupper radiator unit) decreases core resistance and increases coolingairflow, while increased core depth D of lower combined exhaust gas andcharge air cooler unit 80 a (behind the lower radiator unit) increasescore resistance and decreases cooling airflow. Also, increased CAC tube83 spacing S and smaller CAC tube 83 minor diameter m on unit 80 b (bothmeasured in a direction across the face of the core) decrease coreresistance and increase cooling airflow, whereas decreased tube spacings and increased tube minor diameter M on unit 80 a increase coreresistance and decrease cooling airflow. Variations to the core finsalso affect cooling airflow resistance. For example, as shown in FIG. 11with the cores of EGR/CAC units 80 a and 80 b again juxtaposed,increased fin 73 a count per unit vertical distance C, increased finlouver 73 a′ angles A and increased fin thickness T on unit 80 aincrease core resistance and decrease cooling airflow, as compared tothe decreased fin 73 b count per unit vertical distance c, decreased finlouver 73 b′ angles a and decreased fin thickness t on unit 80 b. Theuse of louvered fins 73 a′, 73 b′ increases core resistance anddecreases cooling airflow as compared to flat, dimpled or wavy stylefins.

Each radiator unit 22 a, 22 b in FIG. 9 likewise may have different corestyles, such as core depth, type of fins, fin spacing, fin count, tubespacing and tube count, in the same manner as described in connectionwith the EGR/CAC units.

The core area of the EGR, CAC and radiator cores has a direct effect onairflow management, but in a much more complex manner than the itemsmentioned above. In the embodiment shown in FIG. 9, the charge aircooler core areas may be the same as the radiator core areas, i.e., befully overlapping with respect to cooling air flow. On the other hand,the charge air cooler cores may extend beyond the radiator core areas inone or more directions, i.e., be overhanging or non-overlapping withrespect to cooling air flow, or the radiator core areas may extendbeyond those of the charge air coolers in any direction. The airflowresistance of a given core is inversely proportional to its area.However, the greater the area of a heat exchanger which is overlapped byanother heat exchanger, the greater will be the airflow resistance ofthe two heat exchangers. Increased overlapping results in increasedairflow resistance and increased overhanging results in decreasedairflow resistance through the heat exchangers in the package.

It has been found that the static head loss through the heat exchangerpackage along each airflow path is equivalent. Thus, face velocitiesthat drive convection increase or decrease to achieve this balance. Thesplit radiator and charge air cooler configurations having multipledifferent fin/tube systems provide the flexibility to modify airvelocities for best results. Optimized application-specific results maybe obtained not only through heat exchanger core arrangements, but alsothrough use of different fin/tube systems in each heat exchanger unit.

A further embodiment of the present invention which combines some of thecharacteristics of previous embodiments is depicted in FIG. 12. In amanner similar to the embodiment of FIG. 4, the exhaust gas and heatedcharge air are not combined, but are instead cooled in connectedparallel heat exchangers located adjacent to the radiator. However, in amanner similar to that of the embodiment of FIG. 8, the heat exchangersfor each of the exhaust gas and charge air are split into unitsdownstream and upstream of radiator 22. Recirculated exhaust gas fromline 56 is first cooled in exhaust gas cooler 70′ downstream of radiator22, and, separately, heated charge air from line 42 is first cooled incharge air cooler 80′, in parallel with cooler 70′ and also downstreamof the radiator. The downstream exhaust gas and charge air coolers 70′and 80′, respectively, are connected to form a single unit like thatshown in FIG. 5, except that they are inverted, so that the exhaust gascooler portion is above the charge air cooler portion. As with theprevious description of the embodiment of FIG. 5, the exhaust gas cooler70′ is made of stainless steel or other high temperature-resistantmaterial, since it receives the hotter exhaust gas, and the charge aircooler unit 80′ is made of aluminum. The exhaust gas cooler 70′ andcharge air cooler unit 80′ are located along the lower portion adjacentto and downstream of rear face 23 b of radiator 22, corresponding to theregion in which radiator 22 receives unheated ambient air 60. Thepartially heated ambient air 60 b from the lower portion of radiator 22passes in series through front face 77 a and the tubes and fins of bothexhaust gas cooler 70′ and charge air cooler 80′, and exits as furtherheated ambient air 60 c from the rear face 77 b of coolers 70′/80′.

The partially cooled exhaust gas then exits exhaust gas cooler 70′through line 69 a, where it enters the inlet of second, upstream exhaustgas cooler 70″. The partially cooled charge air exits downstream chargeair cooler 80′ and travels through line 69 b to the inlet of second,upstream charge air cooler 80″. Ambient air 60 passes through the frontface 77 a of both coolers 70″ and 80″, located adjacent the upperportion of the radiator, to respectively cool the exhaust gas and chargeair. The partially heated ambient air 60 a then exits the rear face 77 bof coolers 70″/ 80″ and passes in series through the front face 23 a atthe upper portion of radiator 22. The cooled exhaust gas then exits fromexhaust gas cooler 70″ through line 58, and the cooled charge air exitsfrom charge air cooler 80″ through line 44, and are combined and passedthrough line 46 to engine intake manifold 21.

The upstream exhaust gas cooler 70″ and charge air cooler 80″ are alsoconstructed in connected parallel units 70″/80″ similar to that shown inFIG. 5, except inverted. However, since the exhaust gas is alreadypartially cooled, it does not have an excessively high temperature.Therefore, the upstream exhaust gas cooler 70′ need not be made ofstainless steel or other high temperature-resistant material, and may beconstructed of aluminum, similar to that of charge air cooler 80″. Thelocation and combined height of the downstream exhaust gas and chargeair coolers 70′/80′ and the location and combined height of the upstreamexhaust gas and charge air coolers 70″/80″ are selected so that thedownstream and upstream connected units do not overlap with one another,and so that the sum of the combined heights of the units isapproximately equal to the height of the radiator. As with the otherembodiments previously described, core styles such as core depth, typeof fins, fin spacing and count, and tube spacing and count may be variedand tailored for each unit 70′, 70″, 80′, 80″, to obtain the desiredheat transfer performance.

In a modification similar to those of FIGS. 7 and 9, FIG. 13 shows amodification of the embodiment of FIG. 12 in which the radiator is againsplit into two units 22 a, 22 b, connected by line 62 a, so that thecombined radiator/CAC/EGR cooler package is only two cores deep toreduce package space and improve ambient air flow by fan 90. The frontand rear faces of the vertically matched units 70″, 80″, 22 b and 22 a,70′, 80′, respectively, are in the substantially the same planes, exceptfor any variations in core depth. The heights and widths of thehorizontally matched units, 22 a, 70″/80″ and 70'180′, 22 b,respectively, are substantially the same.

In this system and method shown in FIGS. 12 and 13, only the firstexhaust gas cooler 70′ need be made of stainless steel or other hightemperature-resistant material, while the other three coolers 70″, 80′and 80″ can all be made of lower cost aluminum construction, thusresulting in material cost savings. The heat transfer performance ofthis system and method will be substantially the same as that of FIGS. 8and 9 and far superior to the prior art system and method shown in FIG.2. As with the embodiments shown in FIGS. 4, 6, 7, 8 and 9, the core,tube and fin parameters of the radiator and connected EGR/CAC units inFIGS. 12 and 13 may be varied to modify the air flow as desired throughthe individual heat exchanger units.

Additionally, the direction of flow of engine coolant through theradiator unit(s), and/or the direction of flow of the exhaust gas andcharge air through the ERG/CAC units, may be reversed as desired toachieve desired thermal performance. For example, in the embodiments ofFIGS. 9 and 12, the combined EGR/CAC air flow may be reversed, so thatall of the radiator and combined EGR/CAC units are downflow units.

Cooling air flow through any of the heat exchanger packages shown inFIGS. 4, 6, 7, 8, 9, 12 and 13 may be increased by the use of a fanshroud 88 (FIG. 13) enclosing the area between fan 90 and the heatexchangers, and by moving fan 90 away from the rear face of the heatexchangers so that fan penetration into the enclosure results inoptimized static efficiency. Here, orifice condition on the shroud aswell as the static head loss presented to the fan along each airflowpath of the cooling system determines total airflow. In this mannerthere can be presented to the fan a uniform or non-uniform resistance toairflow to create airflow splits that optimize cooling air approachdifferential and maximize temperature potential where needed to achievesystem performance requirements. While it is difficult to achieve thisin crowded vehicle engine compartments, the heat exchanger packages ofthe present invention facilitate this goal. In particular the splitradiator/split charge air cooler heat exchanger packages of FIGS. 9 and13 provide significant improvement since they are only two cores deep asopposed to single radiator/split charge air cooler arrangements, whichare three cores deep. In addition, splitting the CAC and radiator, withthe use of multiple fin/tube systems, provides a high degree offlexibility in creating airflow splits that can be customized to meetthe needs of each individual application.

Thus, the present invention provides an improved system and method ofcooling an internal combustion engine, including charge air cooling andexhaust gas cooling, which achieves cooling of the charge air and therecirculated exhaust gas to near ambient temperatures, and which allowsthe use of lower cost materials for the charge air and exhaust gascoolers. Improved space saving packaging may be achieved by splittingthe radiator and packaging the combined radiator, CAC and EGR cooleronly two cores deep. Additionally, modifications to the core may be madeto any individual heat exchanger unit within the package to best tailorthermal performance.

While the present invention has been particularly described, inconjunction with a specific preferred embodiment, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

1. A method of cooling engine coolant and charge air from a turbo- orsupercharger in an internal combustion engine comprising: providing aradiator for cooling engine coolant having opposite front and rear corefaces through which ambient air flows, and opposite upper and lower endsadjacent the faces; providing a charge air cooler for cooling charge airhaving upper and lower units, each charge air cooler unit havingopposite front and rear core faces through which ambient air flows, andopposite upper and lower ends adjacent the faces, the upper charge aircooler unit being disposed in overlapping relationship and adjacent tothe upper end of the radiator, wherein one face at the upper end of theradiator is disposed adjacent one face of the upper charge air coolerunit, and the lower charge air cooler unit being disposed in overlappingrelationship and adjacent to the lower end of the radiator with theupper and lower ends of the lower charge air cooler unit being orientedin the same direction as the upper and lower ends of the radiator,wherein the other face at the lower end of the radiator is disposedadjacent one face of the lower charge air cooler unit, each charge aircooler unit having a different core style from the other selected fromthe group consisting of core depth, fin count, and tube spacing, thecharge air cooler units being operatively connected such that the chargeair flows therebetween; flowing the engine coolant through the radiatorto cool the engine coolant; flowing the charge air from the turbo- orsupercharger in sequence through the charge air heat exchanger units tocool the charge air; and flowing cooling air through the heat exchangerassembly such that the cooling air flows in series through the upper endof the radiator and the upper charge air cooler unit, and the coolingair flows in series through the lower charge air cooler unit and thelower end of the radiator, with one of the charge air cooler units beingpositioned upstream of the radiator with respect to cooling air flow andthe other of the charge air cooler units being positioned downstream ofthe radiator with respect to cooling air flow, wherein the upstreamcharge air cooler unit has a lower fin count, lower core depth orincreased tube spacing compared to the fin count, core depth or tubespacing of the downstream charge air cooler unit.
 2. The method of claim1 wherein at least one of the charge air cooler units includes coolingfor recirculated exhaust gas.
 3. The method of claim 1 wherein the upperand lower ends of the upper charge air cooler unit are oriented in thesame direction as the upper and lower ends of the radiator.
 4. Themethod of claim 1 wherein each charge air cooler unit has a differentcore depth from the other, and the upstream charge air cooler unit has alower core depth compared to the core depth of the downstream charge aircooler unit.
 5. The method of claim 1 wherein each charge air coolerunit has a different fin count from the other, and the upstream chargeair cooler unit has a lower fin count compared to the fin count of thedownstream charge air cooler unit.
 6. The method of claim 1 wherein eachcharge air cooler unit has a different tube spacing from the other, andthe upstream charge air cooler unit has an increased tube spacingcompared to the tube spacing of the downstream charge air cooler unit.7. A method of cooling engine coolant and charge air from a turbo- orsupercharger in an internal combustion engine comprising: providing aradiator having upper and lower units for cooling engine coolant, eachradiator unit having opposite front and rear core faces through whichambient cooling air flows, a depth between the front and rear faces, andopposite upper and lower ends adjacent the faces, the radiator unitsbeing operatively connected such that the engine coolant flowstherebetween; providing a charge air cooler having upper and lower unitsfor cooling charge air, each charge air cooler unit having oppositefront and rear core faces through which cooling air flows, and oppositeupper and lower ends adjacent the faces, the upper charge air coolerunit being disposed in overlapping relationship and adjacent to theupper radiator unit, wherein one face of the upper radiator unit isdisposed adjacent one face of the upper charge air cooler unit, and thelower charge air cooler unit being disposed in overlapping relationshipand adjacent to the lower radiator unit, wherein the other face of thelower radiator unit is disposed adjacent one face of the lower chargeair cooler unit, each charge air cooler unit having a different corestyle from the other selected from the group consisting of core depth,fin count, and tube spacing, the charge air cooler units beingoperatively connected such that the charge air flows therebetween;flowing the engine coolant in sequence through the radiator units tocool the engine coolant; flowing the charge air from the turbo- orsupercharger in sequence through the charge air heat exchanger units tocool the charge air; and flowing cooling air through the heat exchangerassembly such that the cooling air flows in series through the upperradiator unit and the upper charge air cooler unit, and the cooling airflows in series through the lower charge air cooler unit and the lowerradiator unit, with one of the charge air cooler units being positionedupstream of a radiator unit with respect to cooling air flow and theother of the charge air cooler units being positioned downstream of theother radiator unit with respect to cooling air flow, wherein theupstream charge air cooler unit has a lower fin count, lower core depthor increased tube spacing compared to the fin count, core depth or tubespacing of the downstream charge air cooler unit.
 8. The method of claim7 wherein at least one of the charge air cooler units includes coolingfor recirculated exhaust gas.
 9. The method of claim 7 wherein eachradiator unit has a different core style selected from the groupconsisting of core depth, type of fins, fin spacing, fin count, tubespacing and tube count.
 10. The method of claim 7 wherein the upper andlower ends of the upper charge air cooler unit are oriented in the samedirection as the upper and lower ends of the upper radiator unit and theupper and lower ends of the lower charge air cooler unit are oriented inthe same direction as the upper and lower ends of the lower radiatorunit.
 11. The method of claim 7 wherein each charge air cooler unit hasa different core depth from the other, and the upstream charge aircooler unit has a lower core depth compared to the core depth of thedownstream charge air cooler unit.
 12. The method of claim 7 whereineach charge air cooler unit has a different fin count from the other,and the upstream charge air cooler unit has a lower fin count comparedto the fin count of the downstream charge air cooler unit.
 13. Themethod of claim 7 wherein each charge air cooler unit has a differenttube spacing from the other, and the upstream charge air cooler unit hasan increased tube spacing compared to the tube spacing of the downstreamcharge air cooler unit.